Somewhere in almost every reefer's first year is the same moment: a coral that looked fantastic in the store goes pale and shrinks back to nothing within a couple of weeks of hitting the tank, and the water parameters are all perfect. Nine times out of ten, the problem isn't chemistry. It's light either too little for the coral to feed itself, or too much, too fast, for a coral that hasn't had time to build up photoprotective pigment.
Quick answer: Corals don't care about watts or Kelvin they care about PAR (Photosynthetically Active Radiation), a measurement of how much usable light actually reaches the coral's tissue. Soft corals want roughly 50-150 PAR, LPS corals want 100-250 PAR, and SPS corals want 200-400 PAR, measured at the coral's actual depth in the tank, not at the water surface. Match the fixture and the placement to those numbers and most "unexplained" coral deaths stop happening.
What PAR actually measures (and why watts don't matter)
PAR is a count of photons in the 400-700 nanometer range hitting a given spot each second, expressed in µmol/m²/s. It's the only real proxy for "how much light is my coral getting," because two fixtures with identical wattage can produce wildly different PAR depending on their optics, LED bin, and how tightly the beam is focused. A 60-watt fixture with narrow optics can out-PAR a 150-watt fixture with a wide, diffuse spread at the same distance which is exactly why watts-per-gallon rules of thumb from the fluorescent-tube era don't translate to LEDs at all.
Kelvin, meanwhile, describes color temperature, not intensity. A light can be dialed to a gorgeous 20,000K blue-white shimmer and still be putting out barely 80 PAR at 20 inches of depth plenty for zoas, nowhere near enough for acropora.
How much PAR does my coral actually need?
This is where placement and lighting decisions actually get made. As a working range:
| Coral type | PAR range | Typical tank zone |
|---|---|---|
| Soft corals (zoanthids, mushrooms, leathers, palythoa) | 50-150 | Lower third, shaded rockwork |
| LPS (hammer, torch, frogspawn, euphyllia, acan) | 100-250 | Mid-tank |
| SPS (acropora, montipora, stylophora) | 200-400 | Upper third, closest to the light |
Two things matter more than the table itself. First, PAR falls off fast with depth and with distance from the light a reading taken at the sand bed can be a fraction of what's hitting the top of the rockwork, so measure (or estimate) at the actual height where the coral will sit, not at the glass or the water surface. Second, euphyllia-type LPS are the outlier: they can acclimate to a surprisingly wide range, from 100 all the way past 1000 PAR, as long as the ramp-up is slow. Most soft and LPS corals, though, will bleach or recede if moved from a low-PAR frag tank straight under a fixture dialed for SPS.
How to place coral by PAR without a meter
A PAR meter (or a rental/borrow from a local reef club) is the accurate way to do this, but most tanks are built the same way even without one: soft corals go low and shaded, LPS fill the middle, and SPS go up near the light where intensity peaks. When adding anything new even to an established tank start it slightly lower or further from center than its "ideal" zone and move it up over 1-2 weeks. That single habit prevents most bleaching-from-shock cases, since it's very rarely the light itself that's the problem so much as the speed of the change.
Comparing AI, EcoTech, Kessil, and Orphek
Four brands dominate the controllable reef LED space right now, and they're not interchangeable they differ meaningfully in spread, intensity, and control ecosystem, not just price.
| Brand / model | Optic style | Typical coverage | Peak PAR (mfr-rated) | Street price (2026) | Best fit |
|---|---|---|---|---|---|
| AquaIllumination Hydra 32HD | Wide-angle lens array, EdgeField optics on the Edge line | ~24"x24" per fixture | High-mid, spread over a wide angle | ~$400-450 new | Mixed reefs wanting broad, even coverage without heavy shadowing |
| EcoTech Radion XR15 G6 Pro | HEI2 hemispherical optics, ~126° spread | Up to ~48"x48" per fixture on the larger G6 | Very high, most even output across a wide area | ~$530-750 depending on retailer | Larger tanks, SPS-heavy aquascapes, anyone wanting the deepest smart-control ecosystem |
| Kessil A360X (Tuna Blue/Sun) | Single dense LED array, no lens diffusion a punchy, shimmery point-source look | ~24"x24" at typical hanging height | High and concentrated near center, falls off faster at the edges | ~$449 (add ~$100 for the WiFi dongle) | Nano and frag tanks, or anyone layering multiple fixtures for shimmer over raw coverage |
| Orphek Atlantik iCon | Compact WiFi-controlled array with a wide spectrum from 380-850nm | Roughly 24"-36" depending on mounting height | Manufacturer-rated near 1000 PAR at ~15" | ~$175-325 depending on promotion/retailer | SPS-dominant tanks on a budget, hobbyists chasing very high PAR per dollar |
A few honest caveats worth sitting with before buying off this table alone. Manufacturer-rated peak PAR numbers are measured under ideal conditions (specific height, specific spot, brand-new LEDs) and will run higher than what you'll see in your own tank once diffusers, age, and mounting height are factored in treat the numbers as relative, not absolute. Street prices also move constantly with sales and bundle deals, so treat the ranges above as a ballpark for comparison shopping, not a quote. And coverage footprint assumes a single fixture at a typical 6-10" hanging height over the water go shallower and coverage shrinks but intensity climbs, go higher and the reverse happens.
If it's not obvious from the table: there's no universally "best" light here. A shallow frag tank running mixed LPS and softies is over-served by a Radion G6 Pro's coverage and intensity, while a deep SPS-dominant display will fight a single A360X for corner coverage no matter how bright it runs. Match the fixture's spread and intensity to the tank's footprint and the coral mix that's actually going in it, and log the PAR readings (or estimated zones) in ReefDiary when you move something, so a future bleaching event has a paper trail back to "did I move this too fast" instead of a guess.
What is PAR in reef tank lighting?
PAR (Photosynthetically Active Radiation) is the measurement of light in the 400-700nm range that's usable for coral photosynthesis, expressed in µmol/m²/s. It's measured with a quantum PAR meter and is a far more reliable predictor of coral growth and health than watts or Kelvin color temperature, since two lights with identical power draw can produce very different PAR depending on their optics and LED quality.
How do I know if my coral is getting too much or too little light?
Bleaching (loss of color, tissue going pale or white) usually signals too much light, too fast the coral is losing its symbiotic algae faster than it can replace them. Browning out, receding tissue, or a coral simply not opening or extending polyps often signals too little light or a placement that's too shaded. In both cases, the fix is usually a placement change with a slow ramp, not a chemistry fix.